The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Many machines require a numerically high reduction ratio gearbox, capable of transmitting substantial power within a limited overall volume. Various long-established methods for all-mechanical drives include a worm-and-wheel gearset, and planetary gearboxes which can be compounded to yield high reduction ratios. One result of adopting these traditional approaches is that the completed reduction gearbox is heavy, or large, when compared to the torque transmitted to the output of such gearboxes. The measures of interest (in lb.-feet units) are therefore pounds-feet of torque per pound weight of the device, or, lb.-ft. per cubic ft. of overall volume.
Awareness of these specific limitations, especially when gearboxes are needed with a reduction ratio ranging from 50:1 to many hundreds to one, prompted a prior design and manufacturing effort into the art of producing incrementing planetary drives. These mechanisms are known as Strain Wave Gearing drives, or, Harmonic Drives.
There are several limitations of the current art with respect to Harmonic Drives. Prior art embodiments of Harmonic Drives, when taken to the largest practical size in terms of torque output and hence physical scale, can be shown to have an upper output torque limit approaching 3,000 lb.-ft. However, some applications require a multiple of 10 times, or even 20 times, or more, of this torque output. It is highly desirable that this is achieved in a single-stage device which avoids the complications of coupling several gearsets together to achieve the required ratio. The detailed description of the cause of the present upper torque limitation is provided here. Clearly, there is a need to further investigate the art of incrementing planetary drives, with an intent of transmitting substantially higher output torques than are currently achieved, and at the same time, improve the specific torque/weight ratio and the torque/volume ratio. This would be a critical design requirement for an aircraft application, for example.
Therefore, there is still a need for improved harmonic drives.